The paper describes a high-temperature superconducting magnetic system (HTS SMS) to equip an experimental stand intended for neuron activity researches under constant and low-frequency magnetic fields up to 1 T. The design of the magnetic system together with its electromagnetic and cryogenic parameters is briefly discussed. The test results of the preliminary experiments conducted in liquid nitrogen at 77 K for two interchangeable magnets are given. The first magnet was manufactured in the form of a double pancake coil wound with 4 mm high HTS tape. The second magnet was made of pure copper wire with no frame and was impregnated with a thermally conducting epoxy resin. The advantages of the HTS pancake coil were demonstrated in comparison with the cryo-resistive solenoid. Low energy consumption of the HTS magnetic system will allow conducting continuous non-invasive monitoring of biological objects in a magnetic field.

In this paper, we present the results of the experimental study of the current-carrying capacity for two high-temperature superconducting samples made of either one 12-mm bare REBCO tape or a soldered stack of five such tapes on current growth rates of up to 350 kA/s. For samples in the form of rings with junctions, the transformer method of current injection was used. Experiments at 77 K showed that the currents of thermal equilibrium with the coolant achieved in the samples very weakly depend on the rate of change in the current and are close to critical ones. At 4.2 K, single mechanical defects of the superconducting layer appeared in the samples with a significant decrease in the local critical current. Current charging at different rates were accompanied by local transitions to the normal state caused by Joule heating of the silver coating when the current bypassed a defect with a resistance of ~1 μΩ at 4.2 K. Repeated measurements at 77 K showed that the resistance of these defects increased to 4 μΩ. This resistance determined the achievable currents at low induction voltages in the samples (low rates of current input). However, when passing through 200 kA/s, the currents reached during repeated measurements at 77 K practically equaled the currents of the first measurements at 77 K before the appearance of defects in the samples in liquid helium.

The current-carrying capacity of second-generation commercial high-temperature superconducting REBCO tapes with a width of 12 mm without a stabilizing copper coating (high-temperature superconductor (HTSC) tapes) in liquid helium has been experimentally investigated at current injection rates up to 350 kA/s. In the experiments, tape samples in the form of rings with junctions are placed in the working volume of a superconducting magnet at 4.2 K. The current in the samples is induced by the transformer method. With an increase in the rate of current injection in the ring-shaped samples, single mechanical defects of the superconducting layer appear in the region of junctions, which causes premature transitions of the samples to the normal state. As a result, the maximum attained currents in the ring samples turned out to be up to 50% lower than the critical currents of short HTSC tape samples at 4.2 K. In conclusion, the analysis of the experimental results is given. Possible explanations for the observed effect are given. In addition, the thermomagnetic stability of two single pancake coils comprised of five isolated turns wound from REBCO tapes supplied from different manufacturers is investigated. The jumps in the magnetic flux are not detected up to an external magnetic field variation rate of 1.7 T/s.

The paper describes a high-temperature superconducting magnetic system (HTS SMS) to equip an experimental stand intended for neuron activity researches under constant and low-frequency magnetic fields up to 1 T. The design of the magnetic system together with its electromagnetic and cryogenic parameters is briefly discussed. The test results of the preliminary experiments conducted in liquid nitrogen at 77 K for two interchangeable magnets are given. The first magnet was manufactured in the form of a double pancake coil wound with 4 mm high HTS tape. The second magnet was made of pure copper wire with no frame and was impregnated with a thermally conducting epoxy resin. The advantages of the HTS pancake coil were demonstrated in comparison with the cryo-resistive solenoid. Low energy consumption of the HTS magnetic system will allow conducting continuous non-invasive monitoring of biological objects in a magnetic field.

In this work, we experimentally investigate the current carrying capacity of single REBCO tapes and stacks made 5 12 mm REBCO tapes with a 25 μm copper stabilizer in liquid helium in comparison with those made of bare tapes with no stabilizer at current ramp rates up to 55 kA/s. The motivation for the research was checking the usability of REBCO stacks as basic sub-elements for high current superconducting cables operating in fast cycling modes at 4.2 K. An original experimental technique was employed to induce the extremely high ramp rates. During the tests, one or 5-folded stacks curled into rings 95 mm dia with different types of joints were charged in the external magnetic field generated by an outer solenoid at ramp rates up to 1.6 T/s. The curled REBCO stacks were either soft-soldered over their entire length or contained local joints only. The maximum screening current induced in the samples during the outer solenoid charging I max was registered. Our experiments showed that the current carrying capacity of the REBCO tapes and stacks was strongly affected by the absence or presence of the copper stabilizer as well as the type of the joint. The reasons for the I max limitation for the copper stabilized and bare samples are also briefly discussed.

Экспериментально исследована токонесущая способность коммерческих высокотемпературных сверхпроводящих REBCO-лент второго поколения шириной 12 mm без стабилизирующего медного покрытия (ВТСП лент) в жидком гелии при скоростях ввода тока до 350 kA/s. В экспериментах образцы лент в виде колец со спаями размещались в рабочем объеме сверхпроводящего магнита при 4.2 K. Ток в образцах индуцировался трансформаторным способом. В процессе повышения скорости ввода тока в образцах-кольцах было обнаружено появление одиночных механических дефектов сверхпроводящего слоя в области спаев, вызывающее преждевременные переходы образцов в нормальное состояние. В результате максимально достигнутые токи в образцах-кольцах оказались до 50% ниже критических токов коротких образцов ВТСП лент при 4.2 K. В заключении приводится анализ результатов эксперимента. Даны возможные объяснения наблюдаемого эффекта. Кроме этого, исследована термомагнитная стабильность двух одинарных галет из пяти изолированных витков, намотанных из REBCO-лент разных производителей. Скачки магнитного потока не были обнаружены вплоть до скоростей изменения внешнего магнитного поля 1.7 T/s. Ключевые слова: сверхпроводимость, высокотемпературные сверхпроводники, ВТСП ленты второго поколения, REBCO-ленты, критический ток, термомагнитная стабильность, скачок магнитного потока.

Here we present the comparative experimental study of the stability of the superconducting state in 4 mm YBCO tapes with copper lamination against local heat disturbances at 77 K. The samples are either directly cooled by immersing a bare YBCO tape into a liquid nitrogen pool or operate in nearly-adiabatic conditions when the tape is covered by a 0.6 mm layer of Kapton insulation. Main quench characteristics, i.e. minimum quench energies (MQEs) and normal zone propagation (NZP) velocities for both samples are measured and compared Minimum NZP currents are determined by a low ohmic resistor technique eligible for obtaining V - I curves with a negative differential resistance. The region of transport currents satisfying the stationary stability criterion is found for the different cooling conditions. Finally, we use the critical temperature margin as a universal scaling parameter to compare the MQEs obtained in this work for YBCO tapes at 77 K with those taken from literature for low-temperature superconductors in vacuum at 4.2 K, as well as for MgB2 wires cooled with a cryocooler down to 20 K.

High-gradient magnetic separator made a good showing at enrichment of low-magnetic ores. However, existing industrial facilities have large dimensions, low specific productivity and high energy costs. Laboratory prototype of high-gradient magnetic separator equipped with superconductor magnet system was developed, manufactured and tested at NRC “Kurchatov Institute”. The device is designed for enrichment of low-magnetic mineral resources, mostly oxidized ferruginous quartzites. The goal of development was both creation of next-generation of separators operating with high-power magnetic fields as well as further progress in applied superconductivity for industrial applications. This paper gives a brief description of the problem, as well as of the process of development, manufacturing and testing the superconducting magnet system. Overall design of the prototype is described, as well as design of collector matrices designed specifically for high-power magnetic field. Next is description of testing process with mineral raw materials obtained from a real industrial enrichment facility. Data on total iron percentage before and after the separation process at the prototype presented, as well as its basic performance characteristics. The results obtained in the course of the project fulfilment can be used in mining industry and metallurgy for manufacturing superconducting magnetic separators of new generation. Such separators will have many advantages comparing with regular separators (with resistive windings) as following: lower energy consumption and less weight, higher induction of the magnetic field in the working gap, possibility to use matrices with coefficient of filling by ferromagnetic precipitating elements at the level of 6-8% with large gaps for pulp passing, higher specific indices due to increased current density in the winding up to 50-100 A/mm2.

High gradient magnetic separation is a promising method for ores enrichment and industrial wastes recycling. The potential of separators based on resistive and permanent magnets is limited by the value of magnetic field and operational costs. LTS magnetic systems require liquid helium and complicated cryogenics. HTS magnets operated in solid nitrogen at 50 K can be a possible solution. In this study, we discuss the conceptual design of an HTS rotary separator prototype with the horizontally oriented rotor axis. The scheme allows to organize a continuous ore processing. The split magnet system consists of two 2G HTS coils on a soft-magnetic yoke with 50 mm room temperature gap. The paper gives the overall design of the magnetic system and the related cryogenic, together with the magnetic fields and forces calculations. The preliminary test results of the ReBCO coil in liquid and sub-cooled nitrogen are also presented.

In this paper we present the results of an experimental investigation of single 12 mm REBCO tapes as well as soft-soldered 5-folded REBCO stacks at current ramp rates up to 320 kA/s. Experimental ring-samples made of one or five HTS tapes with joints were manufactured and charged in external magnetic field. The experiments performed at 77 K showed that the current caring capacity of the samples is very weakly affected by transport current ramp rate. No transitions to the normal state were observed in liquid nitrogen at external magnetic field ramp rates up to 8 T/s. The maximum transport currents achieved by the samples were limited by the thermal equilibrium with the coolant. In contrast, at 4.2 K both single and stacked samples demonstrated preliminary quenches caused by the origination of local defects in the superconducting layers of the HTS tapes with resistances of about 1 mu Ohm at 4.2 K. Reexamination of the damaged samples at 77 K showed that at ramp rates higher than 200 kA/s the currents of the thermal equilibrium with the coolant appeared to be the same before and after the defects appearance.

The international project "NICA" (Nuclotron-based Ion Collider fAcility) is an accelerator complex which is under construction at the Joint Institute for Nuclear Research (Dubna, Russia). Basing on the NICA project demands NRC "Kurchatov Institute" (Moscow, Russia) designed and manufactured two trial 12 kA 1G current leads (CLs) intended for powering of the JINR superconducting magnets test bench. The main requirements for the CLs were: a reliable and robust design, usage of liquid nitrogen from the NICA cooling circuits as a resistive section coolant, low resistance joints, current ramp rates up to 10 kA/s and the total heat load to the 5 K end not exceeding 0.4 W/kA per one CL. An in-situ cold test of the trial 12 kA CLs held at JINR in 2015 demonstrated the operational reliability of our technological approaches. Following the successful test results the serial production of 20 pairs of 10.5 kA HTS CLs with very few design updates for the accelerator powering started. The first 10 pairs were fabricated, tested and shipped to JINR as a part of the NICA commissioning framework in June 2017. All the CLs fulfilled the acceptance test requirements. The production of the remaining 10 pairs is to be finished in 2018. The paper gives an overview of the 12 kA and 10.5 kA HTS CLs' design, discusses their thermal, magnetic and electrical characteristics and presents the acceptance tests results. We also compare our CLs with earlier works by other groups in the context of HTS stack-and-soldering technique, joints' resistances, relative heat loads into the cryogenic environment etc.

High gradient magnetic separation is an effective method for ores enrichment and industrial wastes recycling (including radioactive wastes). The possibilities of separators based on resistive and permanent magnets are limited due to relatively low value of magnetic induction and rather high energy consumption. LTS magnetic systems require liquid helium and complicated cryogenics which can be costly and not always optimal for use at industrial facilities. High-temperature superconductors operated in liquid, sub-cooled and solid nitrogen and equipped with cryocoolers are promising materials that can help expanding industrial application of superconducting devices. In this study, we discuss the design of an HTS rotary separator prototype with the horizontally oriented rotor axis together with the magnetic fields and forces calculations that define prototype working parameters; overall design of HTS-2G coils and preliminary test results of the said coils at different operating temperatures.

A high gradient magnetic (HGM) separator prototype with the 2nd generation high temperature superconducting (2G HTS) magnetic system operated in sub-cooled nitrogen is presently under development at NRC "Kurchatov Institute" (Moscow, Russia). The main goal of the project is an attempt to shift away from the complicated liquid helium cryostats towards simple cryocooler-based nitrogen cryogenics as much more convenient for HGM separators industrial applications. Using of commercial HTS tapes allows to get a sufficient level of magnetic fields and extraction forces with low energy consumption. The expected operational parameters of the device are 1.2-1.5 T in the empty operational gap and up to 3 T on the ferromagnetic filters. In this paper we briefly describe the design of the HTS rotary separator prototype with the horizontally oriented rotor axis and propose different types of ferromagnetic filters intended for weakly magnetic ores enrichment.

Влияние теплоемкости и проводимости нормальной матрицы NbTi композитного сверхпроводника на устойчивость к скачкам магнитного потока

A pair of hybrid current leads (brass + stacked & soldered ReBCO tapes) rated for 12 kA in steady state and for up to 18 kik at pulsed over current conditions was designed, developed and tested at NRC "Kurchatov Institute" (NRC "KI"). During the experiment at LN2 temperature, the current leads (CLs) were successfully charged with 18 kA at 100 A/s ramp rate. To date, as far as we know, this is the highest current capacity achieved for 2G HTS current leads. The feasibility of "stack-and-soldering technique" for 10 kA+ class coated conductor CLs for accelerators and fusion was demonstrated. This paper gives an overview of the leads design and presents the preliminary test results. Detailed studies of magnetic properties and current sharing process for the stacked and staggered HTS joints are also reported. (C) 2017 Elsevier Ltd. All rights reserved.

The stability against magnetic flux jumps has experimentally been studied in the external magnetic field for three samples from NbTi composite superconductors, one monofilamentary and two multifilamentary. A comparison between the experiment and theory of thermomagnetic stability of composite superconductors has been carried out. We have determined threshold values of the rates of the external magnetic fields, starting from which heat capacity and conductivity of the normal composite matrix become determining stabilizing factors. For the first time, the increasing dependence of field of first magnetic flux jump on the rate of the rise in the external magnetic field has been experimentally registered in the superconducting wire for MRI. The reason for this effect is the shunting effect of a high pure copper matrix and the low volume fraction of a superconductor in the composite (~10%).

The thermal stability of NbTi Rutherford-type cables was improved with cold spray technology, namely, by depositing high-heat-capacity coatings onto the surface of the superconductors. Two short samples of identical NbTi Rutherford-type cables with different metallic/ceramic coatings were prepared and tested. The spray particles were deposited onto the cables made of eight monofilamentary NbTi/Cu wires via supersonic velocity impact. The temperature of the process is much lower than the melting point of the sprayed material. The doped sample contained 1 vol.% of large-heat-capacity substance (LHCS) Gd 2 O 3 , whereas the comparison sample did not contain any LHCS. The average heat capacity of the doped sample at 4.2 K was increased more than two times. During the tests, both samples at LHe temperature were subjected to short (~1 ms) electromagnetic disturbances in the transverse constant magnetic field. It was found that the minimum quench energies for the sample with Gd 2 O 3 were 1.4-1.5 times higher than that for the comparison cable without LHCS. The described method is very promising for the stabilization of dense massive windings where the direct heat transfer to the LHe is hampered and the superconductor operates in almost adiabatic conditions.

In this paper we report our recent research on thermal stabilization of low-temperature superconducting magnets by means of large heat capacity substances (LHCS). Two samples (lengths ∼100 m) of NbTi composite wires with additional internal filaments made from intermetallic compound PrB6 (5.9–7.3 vol.%) were produced and tested. The design of the wires was similar to that of the conventional MRI sc wires, except for their smaller diameter (0.835 mm instead of 1.345 mm). Our final goal was the investigation of the possibility to minimize (or even eliminate completely) the necessity of MRI magnets training before their commissioning. The comparative stability measurements showed a twofold increase of the minimum quench energies (MQEs) of the doped wires against short heat disturbances. The magnetic field corresponding to the first flux jump increased by 50%. In MQE tests, the PrB6 heat capacity was fully utilized over the course of a 1 ms heat pulse. In the thermomagnetic stability measurements, the efficiency of LHCS doping was about 75% due to the fast evolution of the flux jumps.

Design of current lead boxes and joint boxes for 2.5 km long St. Petersbubrg HTS DC cable project (2.5 kA, 20 kV) is described. Maximum internal pressure of sub-cooled nitrogen is 1.4 MPa. Both current lead boxes and joint boxes are equipped with terminals for temperature and pressure measurements. Current leads of different polarities have independent electrical insulators. Two current lead boxes and one joint box have been preliminary tested. The first test results are reported.